From f00e6c1d282578b077b87b88f42e701bc40f2fff Mon Sep 17 00:00:00 2001 From: Remi Pommarel Date: Thu, 21 May 2026 11:40:29 +0200 Subject: 9p: Cache negative dentries for lookup performance Not caching negative dentries can result in poor performance for workloads that repeatedly look up non-existent paths. Each such lookup triggers a full 9P transaction with the server, adding unnecessary overhead. A typical example is source compilation, where multiple cc1 processes are spawned and repeatedly search for the same missing header files over and over again. This change enables caching of negative dentries, so that lookups for known non-existent paths do not require a full 9P transaction. The cached negative dentries are retained for a configurable duration (expressed in milliseconds), as specified by the ndentry_timeout field in struct v9fs_session_info. If set to -1, negative dentries are cached indefinitely. This optimization reduces lookup overhead and improves performance for workloads involving frequent access to non-existent paths. Signed-off-by: Remi Pommarel Message-ID: Signed-off-by: Dominique Martinet --- include/net/9p/client.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include') diff --git a/include/net/9p/client.h b/include/net/9p/client.h index 838a94218b59..55c6cb54bd25 100644 --- a/include/net/9p/client.h +++ b/include/net/9p/client.h @@ -192,6 +192,7 @@ struct p9_rdma_opts { * @dfltgid: default numeric groupid to mount hierarchy as * @uid: if %V9FS_ACCESS_SINGLE, the numeric uid which mounted the hierarchy * @session_lock_timeout: retry interval for blocking locks + * @ndentry_timeout_ms: Negative dentry lookup cache retention time in ms * * This strucure holds options which are parsed and will be transferred * to the v9fs_session_info structure when mounted, and therefore largely @@ -203,6 +204,7 @@ struct p9_session_opts { unsigned short debug; unsigned int afid; unsigned int cache; + unsigned int ndentry_timeout_ms; #ifdef CONFIG_9P_FSCACHE char *cachetag; #endif -- cgit v1.2.3